1. Field of the Invention
The present invention relates to a transmission apparatus to be used for satellite broadcasting and satellite communication.
2. Description of Prior Art
Since the sound subcarrier is allocated to 5.73 MHz in conventional satellite broadcasting, the video signal is about 4.5 MHz. The video signal and sound subcarrier are frequency-multiplexed to form a modulation signal and the main carrier has been transmitted after angle modulation. Such a transmission method is described in the report of Investigation for Satellite Broadcast Receiving Technique of Satellite Broadcast Receiver (Target Rating), Part I, issued by the Association of Electromagnetic Wave Technology (June, 1983). In the conventional modulation system, the highest frequency of the video signal is selected to be 4.5 MHz for transmission and if the frequency is raised so as to exceed such a frequency, the spectrum overlaps giving considerable interference because the sideband of the sound subcarrier exists within the range of from 5 MHz to 6.4 MHz. However, in the recent development of high quality display techniques, realization of an improvement in resolution and an enlargement of the aspect ratio is now discussed and it is necessary for such a purpose to increase the amount of information contained in the video signal by expanding its frequency band. As systems for transmitting high definition signals, band compression type MUSE and MAC has been developed. These techniques are described in NIKKEI ELECTRONICS 1987.11.2 (no433)pp189-212, NIKKEI ELECTRONICS 1987.8.10(no427)pp 97-112. However, these systems cannot be applied to the conventional satellite broadcast receiver and therefore it is impossible to enjoy programs of such satellite broadcasting with the conventional receiver. It is therefore expected to provide a signal transmission apparatus which can receive the programs of conventional satellite broadcasting without giving interference to the conventional receiver and realizes a display with a higher resolution and an enlargement of aspect ratio.